Truck goes BOOM - What happened??

[WCPoe]

I was headed home this afternoon and decided to press the go pedal a little hard coming down the home stretch. As I pulled away from a stop sign I gradually rolled into the throttle, it's pulling hard and I figure about the time it gets to third I get a loud Boom.I let off and realize I lost power steering and brakes. I coast down my side street trying to figure out what just happended. The engines running fine, no check engine light but no power steering assisted stuff. It's about that time I also realize I that maybe my trans is defunct.
I pull over shut it off and check under the hood and see the shredded serpentine belt. I figure OK I got one in the truck and could probably get it installed but it's getting dark. But this doesn't explain the no go when I try moving the column shifter through the gears.
Anyway, I'm only about 1/4 mile from the house and one of the neighbors near me offers to help. We go get my John Deere and tow my truck home. I was able to push it in my shop but that's where it sits. I didn't feel like investigating any further tonight because I'm kinda stressed thinking my this might be an expensive fix because my ATS trans is just now a couple of months out of warranty.
Now here's the question??-----> I'm thinking input shaft, anyone have any thoughts???

PS - (See signature) - I didn't think a 2wd would be that hard on a billet shaft would you? It usually justs spins in the lower gears but since I rolled into it I wouldn't see that killing the input shaft.
(Less than 50,000 total miles on the truck and only about 27,000 on the tranny because I retired 3 years ago)